Flash droughts: bridging the understanding between physical definitions and societal impacts

<p>The term &#8216;flash drought&#8217; has become increasingly prevalent in scientific discourse and research on the topic is growing. The corresponding increase in flash drought publications typically presents definitions, mechanisms, detection and monitoring, and forecasting. However, many aspects of flash droughts are less well understood, such as flash drought impacts, especially the socioeconomic and environmental impacts.</p><p>Flash droughts tend to be defined from a hydrometeorological perspective as events of rapid onset, rapid intensification, low precipitation and soil moisture, and high temperature. Yet there are similar, often locally named, phenomena around the world with their own specific characteristics and impacts that could be considered flash droughts. Such events may not match literature or index-specific definitions of flash drought, for example due to their very short duration or anthropogenic drivers. Consequently, they may go undetected or unpredicted in the increasingly common global flash drought products and may not be considered in flash drought research.</p><p>We, the co-authors (a sub-section of the Panta Rhei &#8216;Drought in the Anthropocene&#8217; working group), conducted a survey among peers to collect cases from around the world of alternative names, characteristics and impacts of flash droughts. Many regions were represented in the responses and local nomenclature for flash drought-like events were identified, in particular from Brazil, South Asia, Sub-Saharan Africa and Central America.</p><p>Maps of flash drought hotspots based on hydrometeorological indices often do not indicate whether anything adverse was experienced on the ground, or overemphasise occurrence where events are unlikely. Therefore, we utilised the survey findings and subsequent investigations to &#8216;ground truth&#8217; a flash drought hotspots map. We related hotspots to published case studies of drought impacts or existence of local terms for flash droughts. However, mismatches occurred suggesting there are regions potentially experiencing flash droughts that are either not represented in our survey nor in the literature or there are inaccuracies in flash drought hotspot identification.</p>